I've been watching this thread, it's different and interesting.
You can have more than 12 monitors. If you want to go crazy, there are S1366 boards (the older 9xx i7s) that have up to 7 PCI-E lanes. You could also get Eyefinity-6 cards which support 6 monitors each.
I spent some time poking around the 2 sites you listed, and Theitdepot is actually a pretty decent site. I put together some parts, and I'll explain why I'm using each.
I chose the
Asus P8P67 Pro because it has 4 PCI-E x16 slots, which will allow you to add another Firepro if you decide. It's also just an all-around kick-ass board. It's not Z68, but we're not using any Z68 features anyway, and the depot didn't have one with all the thing's we're looking for. We'll drop the
i7 2600K into it to have plenty of threads to multitask. We'll use the stock Intel cooler as it's reliable, quiet and free, with plenty of cooling at stock speeds. To feed it, we'll add two
G.Skill 8GB PC1600 memory kits. That'll give us 16GB of memory, more than enough for whatever you're doing.
We can put all of that into an
Antec 300 case, which I think is a great case with good cooling, but won't look out of place in an office. Jbaz was right about the power requirements for this build, so a nice reliable
Corsair Builder 500W PSU will give us just what we need.
For storage, there's a few options. We want something reliable, that if the drive fails, you won't experience any downtime. Fortunately, the motherboard supports
RAID 1, which is easy to setup and maintain, and provides an excellent level of redundancy. We could use 2
Deskstar 7Ks to get you 1TB of redundant storage. I would recommend buying a third as an extra drive you can put in if one fails, and of course have an off-site backup plan, but that's beyond the scope of this text. Finally, toss a DVD Burner in it.
LG 24x SATA will work.
Lastly, I would do something I don't think I've ever done and recommend
Windows 7 Ultimate. The ultimate version will give you the ability to join a domain if you need to, and also the ability to run Windows XP mode, which can be important if you work with a lot of different organizations, many online web tools still require IE7. Lastly, it gives you bitlocker, which will allow you to encrypt your entire drive and your backup drives.
That will give you a reliable, fairly quiet PC that is plenty powerful enough for the most demanding analysis and, paired with 3 of your Firepros, easily able to handle 12 monitors.